PALEONUTRITION, METHODS OF
PALEONUTRITION, METHODS OF. There are several kinds of data that inform us about what our ancestors ate. Reviewed in this entry are the data from studies of living primates, archaeology, paleontology, and living hunter-gatherer societies.
The living primates include prosimians, New World monkeys, Old World monkeys, Asian and African apes, and people. Fossil evidence indicates that all primates evolved from insectivore-like mammals that lived some seventy-five million years ago. Primate ancestors may have been those insectivores that moved into the flowering trees of these tropical forests to exploit insects, and then the flowers, fruits, gums, and nectars of those trees. The large number of essential nutrients required in the human diet (forty to fifty essential nutrients) is likely a consequence of the tropical primate diet. Tropical forests are characterized by having a high diversity of species, but a low density of any given species. With a wide variety of food resources, especially fruit, foliage, and insects, ancestral primates were able to obtain many vitamins, minerals, protein, carbohydrates, and fats from their diet. It is metabolically expensive, in terms of energy consumption, for an organism to manufacture its own nutrients (a process called autotrophism). Through mutation and selection, those early primates that reduced autotrophism, and shifted to a dependency on dietary intake to meet their nutrient needs would have gained an energetic advantage, one that could be put to use, for instance, to increase reproduction.
The human primate is unusual in that seeds, grasses, roots, and vertebrate meat are major components of both its modern and ancient diet. Grasses and roots are the category of plant food most often missing from the diet of other primates. Seeds, grasses, and roots have their nutrients protected by cellulose membranes that must be mechanically broken. This can be done by mastication (chewing), or by using technology. Humans, and our hominid ancestors dating back to Australopithecus, possess the anatomy (e.g., small canines, flattened molars, and enlarged pterygoid muscles—those that move the lower jaw from side to side) that allows for a type of chewing called rotary grinding, which can break cellulose. Humans, and our ancestors of the genus Homo, are also dependent on technology (e.g., tools or fire) for food processing. Technology is also required for hunting at a level that makes vertebrate meat a regular part of the diet. For this reason, meat from vertebrates, either hunted or scavenged is not reported as a major component for any nonhuman primate species, although some baboons and chimpanzees regularly hunt mammalian prey.
Archaeology and Paleontology
Archaeological methods focus on the recovery and identification of food remains, of tools and other artifacts used for the acquisition and processing of food, on the analysis of food contained within coprolites (fossilized feces), on the reconstruction of ancient habitats, and on the analysis of hominid fossils. Paleontological data are derived from the kinds and percentages of fossil remains found at a site. Each type of evidence contributes some knowledge, but each has serious limitations. The association of hominid fossil remains with the skeletal remains of other fossil vertebrates may result from geologic forces, such as rivers carrying dead carcasses to a central location or a volcanic eruption burying simultaneously a community of animals, rather than hominid food gathering behavior.
In The Descent of Man (1871), Charles Darwin proposed that hunting large game provided much of the selection pressure for human evolution. That view persisted through the 1960s, but more recent data, based on fossil and archaeological remains and the study of living hunting and gathering people, such as the !Kung and Australian Aborigines, show that gathering and processing of plant foods is the main activity of tropical foragers. Page 36 | Top of Article Moreover, women in living foraging societies provide most of the calories consumed by these people. These observations turned "man the hunter" into "woman the gatherer."
Additional evidence is based on analyses of bone and stone tool material associated with early hominids. Scanning electron microscope images of mammalian long bones dating to 1.7 million years ago show that cut marks produced by stone tools were incised above those made by carnivore teeth and the teeth of known scavengers, such as porcupines. If one assumes that the order of markings reflects the order of use by hunters and scavengers, the hominids were the last to have at the bones, even after porcupines. Early hominids may have been collecting bones for their marrow and brain tissue rather than for any meat still remaining on the surface of the bone. Marrow and brain are high in fat and protein, but few carnivores have the morphology necessary to break open large long bones. The invention of stone tools, first manufactured by hominids about 2.2 million years ago, may have been a dietary adaptation for extracting marrow. Hominids may also have scavenged for larger pieces of meat, perhaps stealing meat from leopards. Leopards carry their kills up into trees and consume their prey over several days. J. A. Cavallo believes that human ancestors may have scavenged these arboreal caches of meat.
Despite the evidence for scavenging animal carcasses and, perhaps, preying on leopards, the bulk of the hominid diet has almost always been from plants. The stone tools of the early hominids may also have been used to process hard to chew plant foods, such as seeds. Studies of the finer details of early hominid dental structure and tooth wear using the scanning electron microscope and tooth wear experiments found that the diet of the early hominids, including Australopithecus and Homo habilis, was largely herbivorous, including softer plant foods (leaves, fruits) as well as the tougher seeds and tubers. Given all the evidence now available, perhaps it is safest to say that the gathering of plants, insects, bird's eggs, and other relatively immobile foods and the scavenging of marrow from carnivore kills typified early hominid food behavior.
Homo erectus added fire to its repertoire of technology. Fire, which may have been used as early as 1.4 million years ago and was certainly controlled by 750,000 years B.P., provided warmth, light, protection, and a new way to process foods. Where and how cooking was invented is a matter for speculation. Cooking, by roasting or boiling, increases the nutritional benefit of many vegetable foods by helping to break down the cellulose of those foods that is indigestible to people. Fire may be used to open large seeds that resist even stone tools. Cooking, especially drying or smoking, helps to preserve foods for storage. Fire may also be used to get foods, especially by driving game towards a convenient killing site. All of these uses of fire did not appear simultaneously, and many appear to be the invention of Homo sapiens rather than Homo erectus. What is certain is that the controlled use of fire was a significant addition to hominid technology with profound consequences for nutritional status.
Coprolites are fossilized feces. Such "hard evidence" might seem to provide unequivocal verification of dietary habits, but coprolites are subject to misinterpretation. First, the coprolite must be identified unambiguously as being from a hominid. Second, coprolites can only verify that a particular substance was eaten. That substance may or may not have been a food item itself, it may have been ingested coincidentally along with a food, such as a seed or insect clinging to an animal or plant. Third, only indigestible substances will be found in feces and those substances must be suitable candidates for fossilization to be preserved in a coprolite. Thus, coprolite analysis may provide a very biased picture of the true dietary intake. Even so, considerable information has been obtained about the diet of prehistoric humans and limited information about the diet of hominid species ancestral to modern people. The animal affinity of desiccated coprolites can be determined by placing the specimen in a trisodium phosphate solution for seventy-two hours. Human coprolites turn the solution an opaque dark brown or black color and no other species produces this effect. Other characteristics of human feces are inclusions of charcoal and the presence of undigested animal parts from a wide variety of species. Charcoal comes from cooking food over a wood fire. Since people cook their food and other animals do not, the presence of charcoal in feces is indirect evidence for a unique human behavior. People also have an eclectic diet compared with most other mammals, so undigested parts from a wide variety of species is another indicator of the human affinities of a coprolite.
More than a thousand paleoindian coprolites from the American Southwest have been identified and analyzed. One group of specimens was collected from Texas sites that date from 800 B.C.E. to 500 C.E., representing the temporary camps of hunting and gathering peoples. By comparing the pollen content of the coprolites with that found in the adjacent soils it was determined that the people had consumed high quantities of flowers. Because the physical characteristics of flower pollens are unique to each species it was possible to determine that flowers of agave, sotol, yucca, prickly pear cactus, gilia, and lead-tree were popular foods. Also found were remains of wild onion bulbs, bark, grasshoppers, fish, small reptiles, and snails. Although not the current cuisine of Texas, this diet is typically human in its diversity of species. The flower pollen even provides a time frame for the occupation of the sites, spring and early summer.
The oldest verified coprolites of a hominid species are from the Homo erectus site of Terra Amata located on the French Mediterranean. These coprolites may be as old as 300,000 B.P. and they are heavily mineralized. They have only a slight reaction to trisodium phosphate rehydration. The specimens contain sand grains, charcoal, and Page 37 | Top of Article mollusk shell fragments. The sand and shell are expected since Terra Amata is a beach front site, and the charcoal helps establish that foods were cooked before consumption (perhaps evidence for a prehistoric clam bake).
Trace element and stable isotope analysis. A general picture of the relative amounts of plant and animal food in the diet may be available from chemical analyses of stable isotopes and trace elements in skeletal remains. For example, the more 13C (a form of the element carbon) in a skeleton the more C4 plants in the diet. C4 plants include the domesticated grains maize, millet, and sugarcane, while C3 plants include virtually all those growing wild in temperate regions. The amount of the stable nitrogen isotope 15N in skeletons indicates an animal's place within the food web. The amount of 15N is higher as more animal protein is included in the diet. Figure 1 illustrates the relationship of these stable isotopes to diet in several mammalian species. This method is most useful when analyzing human skeletons during the transition to agriculture, that is, during the past ten thousand years. A greater dependence on agricultural crops shows up in human skeletons as more C4 plants ( 13C) and, generally, less animal protein ( 15N). Agricultural societies are often stratified socially into higher and lower social classes. Higher classes often have greater access to animal protein. Thus, within agricultural societies the upper classes may have more 15N in their skeletons. This allows archeologists to use stable isotopes as markers of social status.
There are exceptions to the usual 15N indicator of social status. In 1995 Douglas Ubelaker and coworkers analyzed the skeletons from high and low status graves at the archeological site called La Florida in Ecuador. The site dates from 100 to 450 C.E. There were no differences in the levels of protein ( 15N) in these skeletons, but there is a statistically significant difference in the C4 levels between the two groups. The high status group had higher levels of C4. The only C4 plant—the only domesticated plant—that ancient people of highland Ecuador consumed in quantity, was maize. The researchers explain that the extra maize consumed by the elites was in the form of an expensive and politically restricted food called beer. Elites controlled the production and consumption of beer. Maize beer was produced by the chief's household and was doled out to the commoners at feasts in return for their labor. Chiefs also paid tribute to each other in the form of beer and offered copious amounts of beer at royal funerals. Chiefs were buried with many ceramic vessels, and at La Florida 70.5 percent of these were devoted to the brewing and serving of maize beer.
Studies of Living Hunters and Gatherers
All but one-tenth of 1 percent of humans derive their food from some form of agriculture. However, from the time of the Australopithecus until about ten thousand years ago, a period that covers 99 percent of human evolution, all hominids lived in bands and produced food by foraging—the gathering, scavenging, and hunting of wild foods. Most human physical traits, and many behavioral propensities, evolved during the time that hominids lived as hunters and gatherers. This includes current human dietary requirements, adaptations for food acquisition and processing, and biocultural responses to food. Studies of the few remaining cultures of hunting and gathering peoples offer an indirect view of that ancient style of life, now nearly extinct.
Foragers are a diverse group geographically and culturally, ranging from the arctic Inuit and Eskimo, to the tropical forest Ache (Paraguay), to the dry scrub San (Africa), and the desert Australian Aborigines. Yet, the research shows some consistencies in behavior and diet. The diversity of food resources utilized is high among gathering and hunting peoples compared with agriculturists. The !Kung San of southern Africa, for instance, eat 105 species of plants and 144 species of animals (Lee, 1984). The Australian North Queensland Aborigines exploit 240 species of plants and 120 species of animals. The Ache forage on fewer species, about 90 types of plants and animals. Even the Dogrib, residing in the sub-arctic of Canada, gather 10 species of plants and 33 species of animals (Hayden, 1981). That is a small food base for hunters and gatherers, but still a large number relative to agriculturalists who, on a world-wide basis, subsist largely on four species of plants (wheat, rice, potatoes, and maize) and two species of animals (cattle and hogs).
A second common feature is that gathered foods (plants, insects, bird's eggs, turtles, etc.) are the primary subsistence base in most foraging societies. Lee compared fifty-eight forager groups and found that the primary subsistence source was gathering for twenty-nine, fishing for eighteen, and hunting for eleven. Often, the use of many species for subsistence is correlated with the high diversity, low density, or seasonality of food items in the environment. In habitats where low density is combined with the wide dispersal of foods, foragers must be mobile and live in small groups. A small mobile social group is a third typical feature of forager societies. Average group size ranges from nine to fifty-five and average densities range from one to two hundred people per hundred square miles. Mobility ranges from daily movement from camp to camp to seasonal sedentariness at one camp, such as a winter lodge or a summer camp.
A fourth common feature is that all foragers depend on technology to procure, process, and store food. Technology ranges from simple to complex, both in amount and sophistication. Savanna and desert foragers, such as !Kung and Australian Aborigines, use a digging stick to get at roots and tubers that are hidden from view or not possible to extract using hands alone. The digging stick seems simple, but that tool more than doubles the calories available to the people who use it as compared with nonhuman primates living in similar habitats. Bow and Page 38 | Top of Article arrow are used by some groups to hunt large game. At the other extreme of material culture are the Inuit and Eskimo, who possess dozens of pieces of equipment for hunting or fishing, including hooks, spears, sleds, knives, and specialized clothing. The relative complexity of Inuit and Eskimo material culture is required to extract food from a harsh environment.
Food preparation techniques include cooking (such as boiling, steaming, roasting, and frying), soaking, grinding and grating, pounding, drying, fermenting, and putrefying (as in "aged" meat). Many human foods are poisonous prior to preparation by one or more of these techniques. Such toxic raw foods include acorns and horse chestnuts, eaten by many North American Indian foragers and manioc, a root crop, which is a dietary staple of many African societies. The toxins in all these foods are removed by leaching, that is, by boiling them in water and then allowing the food to dry prior to consumption. Rhubarb and cashews, eaten by some people in modern industrial societies, are also toxic until cooked by boiling or roasting. Finally, food storage by drying, caching, and, where possible, freezing or salting is common to many forager groups. It is essential to point out here that dependence on technology for food procurement, the processing of food, and food storage are all behaviors unique to the human species and found universally in all known human cultures.
Sharing and the division of labor comprise a fifth characteristic of foragers. All known living hunters and gatherers share some food, even small game and vegetables in many cultures, and have some division of labor indicating that this is a universal human nutritional adaptation. Sharing and division of labor may best be viewed as behaviors that, first, reduce the effects of unpredictability and variance in food supply, and, second, increase reproductive fitness—that is to say, they increase the healthy development of the individual and his or her likelihood to reproduce. By dividing the social band into working groups based on sex and age, more of the necessary subsistence tasks may be accomplished in a shorter period of time. In tropical and temperate regions, adults may gather plant foods, honey, insects and other small animal foods, and hunt larger animal prey. Children may remain at the camp in an age-graded play group, with older children caring for younger children, or may accompany their parents so as to learn foraging techniques. In extreme environments children may provide significant amounts of foraged food, as they do in Hadza society.
The human diet is unusual because of our high intakes of grasses, seeds, and grains and, for some people, high intakes of meat. No other primate has this mixture of foods in its diet. The interaction between the biological history and the sociocultural behavior of people accounts for our diet. The human place in nature as primates explains our broad requirements of essential nutrients. Fossil and archaeological evidence help to account for the development of the types of foods eaten and the technology needed for food acquisition, preparation, and storage. The study of living hunting and gathering peoples compliments and supports these other sources of evidence. Five features of food, behavior, and demography are typically found in hunting and gathering societies: a high diversity of food types; greater dependence on gathering rather than hunting; small mobile social groups; dependence on technology for acquiring and processing foods; and division of labor and sharing (a sixth feature, stable population size with high infant and childhood mortality balancing fertility, is not discussed here, but see Bogin, 2001). Taken together, the sources of knowledge reviewed here provide the basis for understanding human paleonutrition and the biocultural nature of contemporary human nutrition.
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